1. Field of Art
The present invention relates to an improvement of a door opening/closing device for use in an automobile coating line.
2. Prior Art
Recently the coating work for automobile bodies has been automated for even minute portions of the automobile bodies, particularly doors, due to the introduction of coating robots. Where a door is to be painted automatically by means of a coating robot, it is necessary to open and close the door in order to coat the back of the door. However, providing a special robot for opening and closing of the door causes increased equipment costs. In view of this, there has been proposed a coating robot with a door opening/closing device attached thereto (see U.S. Pat. Nos. 4,342,535; 4,342,536; and 4,498,414).
FIGS. 1 to 5 show an example of such a combination type coating robot. As illustrated therein, an engaging rod 5 and a spray gun 4 are attached to the tip end of an arm 3 of a coating robot 2 disposed adjacent a conveyor line 1. The engaging rod 5, as shown in FIG. 4, is capable of being inserted into a glass slot 7 of a door 6. When the engaging rod 5 is so inserted, the arm 3 is moved horizontally to thereby open or close the door 6. An optical sensor 8 is disposed beside the base end portion of the engaging rod 5. When the optical sensor 8 detects a specific shape (in this case an edge portion 9) serving as an indication of the upper edge of the door 6 during the horizontal movement of the tip end of the arm 3, the arm tip end moves downward, thus causing the engaging rod 5 to be inserted into the glass slot 7. The dash-double dot lines in FIGS. 2 and 3 represent a moving range of the arm 3.
FIG. 5 shows an example of a door opening/closing device having a pivotable engaging rod 10 which represents an improvement over the above prior art. In this device, the engaging rod 10 is pivotable counterclockwise in FIG. 5 from a vertical state about a pin 11, but is not pivotable in the clockwise direction. As the tip end of the arm 3 is moved in the horizontal direction, the engaging rod 10 moves over the upper edge of the door 6 and comes into engagement with the glass slot 7. The use of such a pivotable engaging rod 10 allows the number of operations of the arm 3 to be decreased by one compared to the use of the engaging rod shown in FIG. 4, thus permitting quick opening and closing motion of a door.
Construction of the conventional door opening/closing device is as outlined above, but the following have been pointed out as problems connected with such conventional devices.
In the type wherein the stationary engaging rod 5 is suspended vertically and inserted into the glass slot 7, as shown in FIG. 4, the detection of the edge portion 9 of the door 6 by the optical sensor 8 must be done from a position spaced a distance at least corresponding to the distance of the engaging rod 5 from the edge portion 9 of the door (the height H in FIG. 4), so the optical sensor 8 tends to be deficient in its detecting ability. In addition, since coating material mist is suspended in the air in a coating site, a long-period of operation of the door opening/closing device may allow the mist to adhere gradually to the light-sensitive surface of the optical sensor 8 and deteriorate the detecting ability of the sensor. The resulting erroneous detection by the optical sensor 8 may, in turn, cause malfunctioning of the door opening/closing device.
Furthermore, although use of the type of device having the pivotable engaging rod 10 shown in FIG. 5 allows the height of the optical sensor 8 to be relatively low so that the foregoing deficiency in detecting ability is less serious, there arises the problem that the coated surface which has not yet dried becomes flawed because of contact of the engaging rod 10 with the door 6.